Applying TxRR to Texas Coastal Basins Victoria Samuels CE 394K.2

Background Three state agencies have been assigned the cooperative task of determining just how much water will be needed to maintain our state's streams, rivers, Bays & Estuaries. Currently, the Texas Water Development Board is working with the Texas Parks and Wildlife Department and the Texas Natural Resource Conservation Commission (TNRCC) to collect data and conduct studies on the needs for instream flows and freshwater inflows to the estuarine systems.

TxRR development Estimates runoffs from ungaged watersheds Estimates streamflows on a daily basis Analyzes soil moisture continuously Analyzes direct runoffs by event

TxRR framework Agricultural Research Service (ARS) 12 monthly depletion factors rather than 1 annual factor (used in soil moisture) Soil Conservation Service (SCS) Curve Number Method Parameter Optimization using Newton’s Method Changed to Genetic Algorithm SCS Unit Hydrograph Changed to Gamma function (GAMMADIST function in Excel)

TxRR Water Balance Precipitation P Direct Runoff QD Initial Abstraction I a Infiltration F Maximum Soil Moisture SMMAX = Soil Moisture SM + Soil Retention S Percolation (not modelled) Base Flow QB Stream Flow

How Soil Moisture works - Time Precipitation Event “i-1” Precipitation Event “i” Precipitation Event “i+1” In “i-1” time: In “i” time: SM2 SM1 Time between Precipitation Events = t i

Sequence of Model Before Precipitation Event “i” Soil Moisture depleted from end of event “i-1” to before event “i” Soil Retention increases It Rains! P i at t i Initial abstractions subtracted Runoff produced Excess goes to Infiltration

Soil Moisture Depletion Monthly depletion factors Arrival time of precipitation events SM2 i = SM1 i-1 exp (-  m t i ) SM2 i soil moisture right before i precipitation SM1 i-1 soil moisture right after i-1 precipitation  m monthly depletion factor for month m t i arrival time in days of the i precipitation INPUT:

Soil Retention SMMAX optimized in model S i = SMMAX – SM2 i SMMAX the maximum soil moisture SM2 i soil moisture right before i precipitation S i soil retention at the beginning of i precipitation INPUT: Soil Retention is the dry space in the soil column, the room available for additional moisture or an abstraction.

Direct Runoff QD i = P ei 2 / (P ei + S i ) P ei = P i – Ia i Ia i = abst1 * S i QD i direct runoff from i precipitation P ei effective precipitation Ia i initial abstraction from i precipitation abst1initial abstraction coefficient (usually 0.2) Essentially the SCS Direct Runoff Equation INPUT: P i precipitation from i event abst1, user defined

New Soil Moisture SM1 i = SM2 i + F i F i = P i – Ia i - QD i SM1 i new soil moisture right after i precipitation F i infiltration after i precipitation

Coming Soon Baseflow Calculations – modelled with Soil moisture conditions Daily Streamflow Simulation Applying the Model Acknowledgements: Barney Austin, Dr. Maidment, Richard Gu, Jerry Perales